(1) Field of the Invention
The present invention relates to a high pressure metal vapor discharge lamp, particularly for a metal halide discharge lamp, and a method for manufacturing the same.
(2) Description of the Prior Art
A translucent alumina which withstands corrosive metal halides is used as a tubular body of a discharge tube of the high pressure metal vapor discharge lamp, particularly the metal halide lamp in which the metal halide is sealingly placed, and alumina or cermet is used as end plates adapted to fit electrode support members at end portions of the tubular body. When the discharge tube is produced by assembling these parts together, it is a common practice to bond the end plates by means of a frit (for instance, U.S. Pat. Nos. 3,885,184 and 4,001,625) to the opposite ends of the tubular body made of the alumina which is made translucent through preliminary firing.
However, the use temperature of the discharge tube produced by such a method cannot be sufficiently raised since there is a fear that the frit is corroded with the metal halide, so that the discharge efficacy must unfavorably be suppressed to a level far lower than the theoretical value. In addition, even if such is taken into consideration, only a relatively short durable life can be attained. Therefore, a method which allows easy production of a discharge tube for the metal halide lamp which is high in discharge efficacy and long in the durable life has been being demanded.